This invention relates to an ignition apparatus for an internal combustion engine. More particularly, it relates to an ignition apparatus which can detect misfiring of an engine due to a fault in the ignition system of the engine.
When a problem occurs in the ignition system of an internal combustion engine, so-called "misfiring" can take place in which a cylinder of the engine fails to ignite. When misfiring occurs, uncombusted fuel is exhausted from the engine. The uncombusted fuel then flows into the catalytic converter for the engine, where it undergoes a highly exothermic chemical reaction with the catalyst of the converter. The intense heat of the reaction can damage the converter, and because the converter is raised to a high temperature by the reaction, a fire can result if the converter comes into contact with a flammable material.
Therefore, it is important to detect misfiring in an engine and to stop the supply of fuel to a misfiring cylinder. Misfiring can have various causes, one of which is a failure of the ignition system to properly control the current flowing through the ignition coil for the engine. Some engines are equipped with misfiring sensors which monitor the operation of power transistors for controlling the current of the primary winding of the ignition coil for the engine. Such misfiring sensors are capable of sensing misfiring due to a malfunction of the power transistors or of parts which control the operation of the power transistors.
However, misfiring can also be caused by a problem between the power transistors and the spark plug, such as an open circuit or a short to ground in the cables which connect the spark plugs to the distributor. A conventional misfiring sensor can not detect misfiring due to such problems, since these problems do not necessarily affect the operation of the power transistors.